Oxidising agents for elastomer bonding compositions

ABSTRACT

Compositions comprising at least one copper salt, and an aromatic nitroso compound precursor are provided. The copper salt may oxidize the aromatic nitroso compound precursor to provide an aromatic nitroso compound. The compositions may find utility in polymer to metal, in particular, rubber to metal bonding. The aromatic nitroso compound precursor may be a nitrosobenzene/dinitrosobenzene precursor. The nitrosobenzene or dinitrosobenzene precursor may be at least one of a quinone oxime or a quinone dioxime.

BACKGROUND

1. Field

The present invention relates to the use of oxidising agents in adhesivecompositions suitable for use in polymer to substrate, such as elastomerto substrate, for example polymer-to-metal, such as elastomer-to-metalincluding rubber-to-metal bonding applications. The oxidising agentstransform a latent cross linking agent into a species capable ofactively crosslinking elastomers comprising diene and or allylicfunctional groups and are suitable for use in the above bondingapplications and in particular in rubber to metal bonding applications.

2. Brief Description of Related Technology

Polymer to metal and in particular rubber to metal bonding has beenpractised for many years. There are many applications for formulationswhich achieve polymer or rubber to metal bonding. Rubber to metalbonding is widely used to bond different metals to a natural orsynthetic rubber. Polymer to metal bonding is carried out for manyreasons.

One aspect of rubber to metal bonding is to combine the structuralstrength of the metal with the elastomeric properties of the rubber.Accordingly, metal and polymers such as rubber, in particular, are oftenbonded to each other for impact absorption applications, such asbearings, wheels, shock absorbers, moving arms, etc. Such components canbe utilised on a very small scale, for example in PC components or on avery large scale for example in constructions such as bridges andbuildings. Noise reduction may also be achieved by utilising metal torubber bonding. It is accepted that tremendous forces can be experiencedby any component which comprises metal and rubber bonded together.Accordingly, it is desirable to provide metal to rubber bonding that canwithstand significant forces such as compressive or extensive forces,including shocks, without having the metal or the rubber separate fromeach other. There are many other applications where rubber to metalbonding is desirable, for example in tyre production where internal wirereinforcements for the tyre are bonded to the rubber of the tyre.

Generally, an adhesive formulation is provided to bond a selected rubberto a selected metal substrate. Traditional rubber-to-metal bondingtechnology consists of a primer layer and also an adhesive layer,forming an overall 2-coat system. The primer system generally consistsof solutions or suspensions of chlorinated rubber and phenolic resinscontaining reactive groups, and also pigments such as titanium dioxide,zinc oxide, carbon black, etc. The primer is generally applied as a thinlayer onto a treated (cleaned) surface of a metallic component such as atreated steel component for example a component that has been gritblasted or chemically treated.

The adhesive layer can consist of a large range of elastomeric materialssuch as rubber materials and cross-linkers. These include, but are notrestricted to, chlorinated and bromochlorinated rubbers, aromaticdinitrosobenzene compounds and bismaleimide as cross-linkers, xylene,perchloroethylene and ethylbenzene as solvents, and also some inorganiclead or zinc salt.

The most common cross-linking agents that have been employed inrubber-to-metal bonding technology are aromatic nitroso compounds, suchas p-dinitrosobenzene. The mechanism of cross-linking to an alkene groupwithin a rubber, such as a diene or allylic moiety, is by means of apericyclic reaction.

In the many fields where rubber to metal bonding is employed there arenumerous opportunities to address several types of problems, includingbond strength and durability, sample preparation, ease of application ofthe adhesive, single coat versus two-coat systems, reduced toxicity andimproved properties for the environment, to name a few.

Dinitroso compounds are ordinarily used in rubber bonding formulations.The high toxicity of these dinitroso compounds, in particular, posesserious handling and safety problems. In addition dinitroso compoundscan exhibit fuming at elevated temperatures which aggravates the problemof mold fouling.

Different formulations for rubber to metal bonding are the subject ofmany patent publications. Lord Corporation has conducted studies in thearea of use of oxime and dioxime materials. For example as set out inEuropean Patent Document No. EP0287190, an adduct of any aromaticdioxime (quinone dioxime is preferred) and a polyisocyanate (toluenediisocyanate is preferred) is formed in a ratio of greater then 2:1, andrubber to metal bonds formed.

U.S. Pat. No. 4,581,092 discloses an adhesive system that includes abutyl rubber, a polyisocyanate compound, and at least one of a nitrosocompound and an oxime compound, with the oxime compound requiring theadditional presence of an oxidizing agent, including Pb₃O₄, PbO₂, MnOand V₂O₅. The oxidizing agent is present at a level of 2 to 3 parts perpart of aryl dioxime compound.

U.S. Pat. No. 3,824,217 discloses combining an oxime compound with anexcess of a polyisocyanate compound, so that all oxime groups react withisocyanate. The resulting compound could be used in compositions forbonding rubbers to primed metal substrates. U.S. Pat. No. 3,859,258 alsoreports an oxime-isocyanate product for use in rubber to metaltechnology.

U.S. Pat. No. 4,994,519 is directed to a quinone dioxime system that hasrubber to metal bonding performance without the use of an oxidant, whenpresent with chlorinated rubber, brominated polybutadiene, carbon blackand from 5 to 25% by weight of ground sulfur. The use of free sulfurhowever is not widely accepted within the industry.

U.S. Pat. No. 4,031,120 describes a composition comprising an isocyanatefunctional organosilane, in combination with a polyisocyanate and anaromatic nitroso compound. The resulting system is described as aone-coat adhesive for bonding a variety of elastomeric materials tometals and other substrates. In this patent an isocyanate is reactedwith a functional alkoxy silane such as amino, hydroxy, or mercapto.

Notwithstanding the state of the art it would be desirable to providealternative elastomer bonding compositions addressing the issues raisedabove, such that improved consumer choice results.

SUMMARY

The present invention provides compositions suitable for polymer tosubstrate, such as elastomer to substrate, for example elastomer tometal bonding such as for use in rubber to metal bonding. Natural andsynthetic rubbers are included within the term rubber as used herein.The rubber may be a blended material.

In one aspect the present invention provides for a bonding compositioncomprising:

-   -   a) at least one copper compound; and    -   b) at least one aromatic nitroso compound precursor.

The copper compound may oxidise the at least one aromatic nitrosocompound precursor to generate an aromatic nitroso compound in-situ.

As will be appreciated by a person skilled in the art, compositions ofthe present invention may further comprise adhesion promoting agents.The adhesion promoting agent may promote crosslinking between thearomatic nitroso compound and the elastomer substrate or may provide forimproved adhesion to a substrate. For example, the adhesion promotingagent may be a silane.

As used herein, the term aromatic nitroso compound precursor refers toany compound that is capable of being transformed into an aromaticnitroso compound with at least one nitroso group. The aromatic nitrosocompound precursor may comprise any aromatic oxime, aromatic dioxime andcombinations thereof. The aromatic nitroso compound precursor may be themono- or dioxime of a compound selected from the group consisting of:

As will be appreciated by a person skilled in the art, the diketonestructures disclosed above may optionally be substituted one or moretimes, for example with at least one of C₁-C₂₀ alkyl, C₁-C₂₀ cycloalkyl,C₁-C₂₀ alkoxy, C₆-C₂₀ aralkyl, C₆-C₂₀ alkaryl, C₆-C₂₀ arylamine, C₆-C₂₀arylnitroso, cyano, amino, hydroxy, halogen and combinations thereof.Such substitutions may be possible provided there is no interferencewith effective bonding or curing of the compositions. For example,provided there is no interference with the generation of an aromaticnitroso compound in-situ.

Desirably, the aromatic nitroso compound precursor is selected from thegroup consisting of p-benzoquinone dioxime (QDO), naphthoquinonedioxime, toluquinone dioxime, diphenoquinone dioxime, diquinoyl dioxime,dibenzoyl dioxime and combinations thereof. The above list serves as ageneralised example only and other aryl oximes and dioximes are possibleand embraced by the present invention.

The at least one aromatic nitroso compound precursor of the compositionof the present invention may comprise a nitrosobenzene precursor. Thenitrosobenzene precursor may be a mononitrosobenzene precursor, adinitrosobenzene precursor, or combinations thereof. It will beappreciated that the nitrosobenzene precursor may form a nitrosobenzeneor dinitrosobenzene structure in-situ upon oxidation.

As will be appreciated by a person skilled in the art, references tonitrosobenzenes and nitrosobenzene precursors include nitrosobenzene andnitrosobenzene precursors that may optionally be substituted one or moretimes with at least one of C₁-C₂₀ alkyl, C₁-C₂₀ cycloalkyl, C₁-C₂₀alkoxy, C₆-C₂₀ aralkyl, C₆-C₂₀ alkaryl, C₆-C₂₀ arylamine, C₆-C₂₀arylnitroso, cyano, amino, hydroxy, halogen and combinations thereof.Such substitutions may be possible provided there is no interferencewith effective bonding or curing of the compositions. For example,provided there is no interference with the generation of anitrosobenzene in-situ.

Desirably, the nitrosobenzene precursor comprises p-benzoquinone oximeor p-benzoquinone dioxime (QDO). It has been found that such structuresassist in the formation of desirable bonds. For example, thenitrosobenzene precursor may be selected from the group consisting of:

or combinations thereof.

QDO is generally used as a vulcanizing agent for EPDM(ethylene-propylene diene monomer) to improve heat resistance. It isalso used as a rubber to metal adhesion promoter and as a curing agent.

The aromatic nitroso compound precursor of the composition of thepresent invention may comprise at least one silane moiety (an aromaticnitrososilane precursor). The silane moiety may be an alkoxysilane.Advantageously, alkoxysilanes may enhance adhesion to particularsurfaces, for example metal surfaces. For example, the aromaticnitrososilane precursor may be one of the general formula:

where ‘a’ can be 1-3 and ‘b’ can be 0-2; but if a=3, b=0; or if a=2,b=1; so that at least one alkoxy group is present;R¹ can be selected from the group consisting of H, C₁-C₂₄ alkyl, C₃-C₂₄acyl, preferably from C₁-C₄ alkyl and wherein when a≧1 at least one R¹is not hydrogen; andR² can be selected from C₁-C₂₄ alkyl and C₃-C₂₄ acyl, preferably fromC₁-C₄ alkyl;n can be 1-5;X can be O or S;Y can be —O, —S, or —NH_(x) (where x=1 or 2); andR³ can be a moiety comprising a nitroso aromatic compound precursor.

R³ may be a moiety comprising nitrosobenzene, or a nitrosobenzeneprecursor. Preferably, R³ comprises a quinone dioxime or quinone oximemoiety. Such materials are readily available from commercial suppliers.

R¹ may be selected from C₁-C₂₄ alkyl, C₃-C₂₄ acyl. R¹ may be selectedfrom C₁-C₂₄ alkyl, C₃-C₂₄ acyl and ‘a’ may be 3. X may be O. Y may be Oor —NH_(x) (where x=1). R¹ may be selected from C₁-C₄ alkyl, X may be Oand ‘a’ is 3. R¹ may be selected from C₁-C₄ alkyl, X may be O, Y may beO and ‘a’ may be 3. R¹ may be selected from C₁-C₄ alkyl, X may be O, Ymay be —NH_(x) (where x=1) and ‘a’ may be 3. R¹ may be selected fromC₁-C₄ alkyl, X may be O, Y may be O, ‘a’ may be 3 and R³ may be a moietycomprising nitrosobenzene. Other suitable nitrososilanes are disclosedin U.S. patent application Ser. No. 12/055,908, the disclosure of whichis hereby incorporated herein by reference.

The at least one aromatic nitroso compound precursor may be present inan amount of 1 to 20% w/w of the total composition. Suitably, the atleast one aromatic nitroso compound precursor may be present in anamount of 1 to 10% w/w, for example 2 to 7% w/w. The at least onearomatic nitroso compound precursor may be present in 3% w/w of thetotal composition.

In the compositions of the present invention the oxidant is a coppercompound. For example, the copper compound may be a Cu(I) or Cu(II)compound. The copper compound may be a Cu(0) compound which may oxidisein situ to a Cu(I) or Cu(II) compound. The copper compound may bemetallic copper, copper salts, copper oxides or combinations thereof.Suitable copper compounds may be selected from the group consisting ofcopper nanopowder, CuO, Cu₂O, CuSCN, Cu(SCN)₂ and combinations thereof.The copper compound may be CuSCN, Cu(SCN)₂ or combinations thereof. Thecopper may be CuSCN. The oxidant may be copper thiocyanate.

The copper compound may be present in an amount of 1 to 20% w/w of thetotal composition. Suitably, the copper compound may be present in anamount of 1 to 10% w/w, for example 2 to 7% w/w. The copper compound maybe present in 4% w/w.

The copper compound (or oxidant) may be encapsulated. The encapsulantmaterial may be selected from the group consisting of hard, polymerisedmaterial, gelatin or resin. For example, suitable resins may compriseurea/formaldehyde resin.

A general scheme for the oxidation of quinone dioxime to thedinitrosobenzene species using a copper oxidant is shown below:

Compositions suitable for bonding metal to rubber may be formulatedutilising appropriate amounts of a copper oxidant according to thepresent invention.

Compositions of the present invention may be one-part compositions.Compositions of the present invention may be two-part compositions.

The compositions of the present invention may further comprise asuitable carrier vehicle for the aromatic nitroso compound precursor andor copper salt. It will be appreciated that any suitable carrier vehiclemay be utilised. It is desirable that the carrier vehicle isenvironmentally friendly. For example, the carrier vehicle may be anaqueous-based vehicle. Such compositions of the invention are suitablefor use in bonding a substrate such as a metal substrate to a polymersubstrate, such as an elastomer, for example a natural or syntheticrubber.

The compositions of the present invention provide for elastomer tosubstrate bonding, for example elastomer to metal bonding. Compositionsof the present invention may assist in the formation of good rubber tometal bonds. Such compositions can be applied at the interface betweenthe rubber and the metal substrates, and may assist in developing strongand durable bonds during the rubber curing process.

Compositions comprising an aromatic nitroso compound precursor with acopper oxidant may overcome the problems associated with the prior artdiscussed above. Furthermore, the compositions of the invention may beless toxic. This is particularly important prior to vulcanisation.

Compositions of the present invention may find utility in anyapplication where it is desirable to form an aromatic nitroso compound,for example a nitrosobenzene moiety, in-situ. Similarly, compositions ofthe present invention may find utility in any application where it isdesirable to form an aromatic dinitroso compound, for example adinitrosobenzene moiety, in-situ.

Compositions of the present invention may find utility in bonding asubstrate to a natural or synthetic rubber. For example, thecompositions may be used for applications where bonding metal to naturalor synthetic rubber is required. In particular, compositions of thepresent invention will provide for in-situ generation of anitrosobenzene moiety or a dinitrosobenzene moiety.

For example, to achieve good bonding it may be desirable for thecompound to react in-situ to form a nitroso aromatic moiety comprising ahydroxy group. The nitroso aromatic moiety comprising a hydroxy groupmay be a para-nitrosophenol moiety. The phenolic moiety present may helpto anchor the para-nitrosophenol moiety to a metal surface.para-Nitrosophenol may be generated in-situ from the oxidation ofquinone mono-oxime as shown below:

By incorporating aromatic nitroso compound precursors, the compositionsof the present invention eliminate the undesirable need to formulatecompounds comprising free nitroso groups in adhesive compositions.In-situ oxidation of the aromatic nitroso precursor during thevulcanisation process, which is the phase where bond formation takesplace, is desirable.

The compositions of the present invention possess a number ofadvantages. For example, an adhesive composition absent dinitrosobenzenemay be formulated and stored. Such formulations are easily andconveniently applied to substrates in a standard manner. Convenienttechniques for application may also be used, for example spraying ordipping. Compositions of the present invention may also have reducedtoxicity as compared to conventional dinitrosobenzene formulations.

In addition, compositions according to the present invention are capableof curing to provide excellent bond strengths. For example, in rubber tometal bonding tests to determine the bond strength of the compositionsof the present invention, up to 80% rubber failure was observed.Furthermore, the resultant bonds have hot water resistance.

In a further aspect, the present invention extends to a process forbonding two substrates together comprising applying a compositionaccording to the present invention to at least one of the substrates andbringing the substrates together so as to form a bond with thecomposition.

The at least one substrate may comprise a polymer, such as elastomer tobe bonded to another substrate. The at least one substrate may comprisea natural or synthetic rubber to be bonded to another substrate. Thefirst substrate may comprise a polymer, for example an elastomer, suchas a natural or synthetic rubber, and the second substrate may comprisea metallic substrate. The first substrate may comprise a metallicsubstrate to which a composition according to the present invention isapplied, and the second substrate may comprise a polymer, such aselastomer, for example a natural or synthetic rubber.

The nitroso aromatic compound of the composition of the presentinvention may become anchored to the rubber substrate.

The rubber substrate may be vulcanised or crosslinked prior to bondingto the second substrate. Alternatively, the rubber substrate may bevulcanised or crosslinked concurrently with bonding to the secondsubstrate. The second substrate may be a metal.

The present invention allows for bonding of polymers, such aselastomers, for example natural or synthetic rubbers, to othersubstrates such as metals, as the nitroso groups can react withpolymers, in particular a polymer with diene or allylic functionalitywithin the polymer chain. Reaction of a nitroso group and an allylicgroup on the polymer occurs via an alder-ene reaction. Such a reactionproduces a variety of cross-links, for example between the nitroso groupand a rubber material.

The present invention provides very good adhesion between elastomericmaterials, such as rubber compositions, and metals.

Many different metals may be treated with the composition described inthis invention, and may be bonded to polymers, such as elastomericmaterials. These metals include, but are not limited to, zinc and zincalloys such as zinc-nickel and zinc-cobalt alloys, metal substrateshaving zinc-containing coatings, steel and in particular cold rolled andcarbon steel, aluminium and aluminium alloys, copper and copper alloyssuch as brass, and tin and tin alloys including metal substrates havingtin-containing coatings.

In a further aspect, the present invention relates to an assemblycomprising a first substrate and a second substrate bonded together by acomposition according to the present invention. Desirably, one of thesubstrates is an elastomer, such as a natural or synthetic rubber. Thesecond substrate may be a metal. The invention further extends to a cureproduct comprising a polymer, for example an elastomer, such as anatural or synthetic rubber and a composition according to the presentinvention.

Where suitable, it will be appreciated that all optional and/orpreferred features of one embodiment of the invention may be combinedwith optional and/or preferred features of another/other embodiment(s)of the invention.

DETAILED DESCRIPTION

It should be readily apparent to one of ordinary skill in the art thatthe examples disclosed hereinbelow represent generalised examples only,and that other arrangements and methods capable of reproducing theinvention are possible and are embraced by the present invention.

The compositions of the present invention may suitably comprise anyadditives conventionally used in common rubber formulations which do notoppose or prevent in situ formation of aromatic nitroso compounds, forexample nitrosobenzene or dinitrosobenzene. Illustrative of suchadditives are reinforcing carbon blacks; inactive fillers such ascalcium carbonates, chalks, talcs, or metal oxides; accelerator systems;vulcanization retarders; promoters such as zinc oxide or stearic acid;plasticizers such as aromatic, paraffinic, naphthenic and syntheticmineral oils; ageing, light-protecting ozone-protecting, fatigue,coloration, and processing auxiliaries and sulfur. Commonly theseadditives may be present at a quantity of about 0.1 parts to about 80parts per 100 parts by weight of the rubber composition.

Generally, it is desirable that bonding is achieved during avulcanisation step. Suitable vulcanisation methods include compressionmoulding, transfer moulding, injection moulding and autoclave heating,for example with steam or hot air. For example semi-solid rubber can beinjected into a mould. The semi-solid rubber is then cross-linked into afully cured rubber and the bond with the substrate is formed at the sametime.

The curing system should be stable for use. More specifically, thecuring system should be resistant to sedimenting. Accordingly, it isdesirable that the curing system has a low tendency to sediment.

Furthermore, the curing system should be easy to apply. For example, itshould be convenient to apply by any suitable dispensing system. It isalso desirable that it dries quickly so that components can be handledwithout applied material running off and/or fouling productionequipment. It is also desirable that the curing system shows goodwetting properties for ease of application and spreading, for instance.

It is also desirable for the composition to have good curing strengths.This curing should be achieved independently of the type of elastomer(rubber) employed and also independently of the type of substrate. Itwill be appreciated that some rubbers are blended materials andaccordingly it is desirable that good curing is achieved with suchblended materials. Suitably consistent curing is achieved under variousprocess parameters.

It is desirable that the bonds and in particular the rubber/metal joint,are durable under high pressure and even if exposed to an aggressiveatmosphere, for example, a hot liquid such as oil. The bonds should alsobe durable against relatively high mechanical stress.

EXAMPLES

Prior to application of the primer and adhesive layers, the metalsurface to be coated may be cleaned to allow better adhesion. Forexample, cleaning with solvent or alkaline material. Application canthen be conducted by a variety of methods, including dipping, spraying,brushing or wiping the solution onto the metal.

The primer is applied as a thin layer onto a treated (cleaned) surfaceof a metallic component such as treated steel component. The adhesivelayer is applied as a thin layer on top of the dry primer layer.Compositions embraced by the present invention are set out below:

Primer Formulation Example

Compound identity % by weight Pergut S130 ^((a)) 8.3 Titanium Dioxide5.1 Carbon Black 1.3 Aerosil 200 ^((b)) 1.3 Zinc Oxide 1.7 ElaztobondA250 ^((c)) 4.2 SP1055 ^((d)) 5.1 Methyl Isobutyl Ketone 63.0 Xylene10.0 ^((a)) Chlorinated Rubber (from Bayer Material Science); ^((b))Fumed Silica (from Evonik); ^((C)) Phenol Formaldehyde Resin (from SIGroup); ^((d)) Phenolic Resin (from SI Group)Adhesive Formulation 1:

Compound identity % by weight Pergut S130 ^((a)) 2.0 Xylene 69.6Titanium Dioxide 2.0 Heucophos ZPA ^((b)) 2.1 Zinc Oxide 4.2Chlorosulfonated Polyethylene ^((c)) 5.5 HVA-2 ^((d)) 1.14,4-Diphenylbismaleimide 1.1 Hydrophobic Fumed Silica 0.8 Carbon Black4.5 Quinone Dioxime 3 Cu₂O 4 ^((a)) Chlorinated Rubber (from BayerMaterial Science); ^((b)) Zinc aluminium orthophosphate hydrate (fromHeucotech Ltd.); ^((c)) Hypalon 40S (DuPont Performance Elastomers);^((d)) N,N-m-Phenylene Bismaleimide.Adhesive Formulation 2:

Compound identity % by weight Pergut S130 ^((a)) 2.0 Xylene 69.6Titanium Dioxide 2.0 Heucophos ZPA ^((b)) 2.1 Zinc Oxide 4.2Chlorosulfonated Polyethylene ^((c)) 5.5 HVA-2 ^((d)) 1.14,4-Diphenylbismaleimide 1.1 Hydrophobic Fumed Silica 0.8 Carbon Black4.5 Quinone Dioxime 3 CuO 4 ^((a)) Chlorinated Rubber (from BayerMaterial Science); ^((b)) Zinc aluminium orthophosphate hydrate (fromHeucotech Ltd.); ^((c)) Hypalon 40S (DuPont Performance Elastomers);^((d)) N,N-m-Phenylene Bismaleimide.Adhesive Formulation 3:

Compound identity % by weight Pergut S130 ^((a)) 2.0 Xylene 69.6Titanium Dioxide 2.0 Heucophos ZPA ^((b)) 2.1 Zinc Oxide 4.2Chlorosulfonated Polyethylene ^((c)) 5.5 HVA-2 ^((d)) 1.14,4-Diphenylbismaleimide 1.1 Hydrophobic Fumed Silica 0.8 Carbon Black4.5 Quinone Dioxime 3 Cu nanopowder 4 ^((a)) Chlorinated Rubber (fromBayer Material Science); ^((b)) Zinc aluminium orthophosphate hydrate(from Heucotech Ltd.); ^((c)) Hypalon 40S (DuPont PerformanceElastomers); ^((d)) N,N-m-Phenylene Bismaleimide.

Bond strengths of 9 to 12 N/mm were observed for Adhesive Formulations1-3. Up to 80% rubber failure was also recorded.

Adhesive Formulation 4:

Compound identity % by weight Pergut S130 ^((a)) 2.0 Xylene 69.6Titanium Dioxide 2.0 Heucophos ZPA ^((b)) 2.1 Zinc Oxide 4.2Chlorosulfonated Polyethylene ^((c)) 5.5 HVA-2 ^((d)) 1.14,4-Diphenylbismaleimide 1.1 Hydrophobic Fumed Silica 0.8 Carbon Black4.5 Quinone Dioxime 3 CuSCN 4 ^((a)) Chlorinated Rubber (from BayerMaterial Science); ^((b)) Zinc aluminium orthophosphate hydrate (fromHeucotech Ltd.); ^((c)) Hypalon 40S (DuPont Performance Elastomers);^((d)) N,N-m-Phenylene Bismaleimide.

Bond strengths of 9.5 to 10 N/mm were observed for Adhesive Formulation4. Up to 80% rubber failure was also recorded.

Tests were carried out using natural rubber of the followingcomposition:

Rubber Composition

Ingredient Parts* Natural Rubber ^((a)) 100 Zinc Oxide 3.5 Stearic Acid2 Carbon Black ^((b)) 40 Naphthenic Oil (low viscosity) ^((c)) 51,2-Dihydro-2,2,4-Trimethylquinoline ^((d)) 2N-(1,3-dimethylbutyl)-N'-phenyl-p- 1 phenylenediamine ^((e)) HydrocarbonWaxes ^((f)) 2 CBS ^((g)) 0.7 Sulfur 2.5 ^((a)) NR SMR CV 60; ^((b)) SRFN762 black; ^((c)) Oil Strukthene 410; ^((d)) Flectol H; ^((e))Santoflex 13 (HPPD); ^((f)) Sunproof Improved Wax; ^((g)) Vulcanisationaccelerator, N-Cyclohexyl-2-benzothiazole. *All parts are parts byweightTesting Methods

To assess the efficacy of the adhesive systems described of the presentinvention in bonding rubbers to metal surfaces, a series of tests wereperformed according to the ASTM 429-B standard adjusted to a 45° angle.Metal substrates (2.54 cm (1 inch) wide, 10.16 cm (4 inch) long panelsor coupons) were coated with the adhesive and adhered to natural rubberin a vulcanisation process. The natural rubber compositions weresulfur-cured compositions as set out in the Formulation tables.

The metal substrates were ultrasonically cleaned in an automated aqueousalkaline cleaner, rinsed with de-ionized water and blow-dried with hotair. The substrates may also be grit-blasted using a suitable abrasiveagent.

Before application of the adhesive, 2.54 cm (one inch) of length (andalso 2.54 cm wide (one inch)) on both ends of the metal coupon wasmasked to prevent that region being available for bonding to the rubber,leaving a central area of 2.54 cm (1 inch) in width and 5.08 cm (2inches) in length available to bond to the rubber.

In the bonding operation of the present invention, the compositions areapplied to metal substrates by either a dipping, spraying or brushmethod to ensure an even coverage, preferably after the substrate hasbeen cleaned.

Drying may be carried out under ambient conditions, that is roomtemperature. Solvent evaporation rate can be increased by heat, forcedair or both.

A layer of uncured rubber was then placed on each coupon and cured in astandard hydraulic vulcanisation press for a period of time specified bythe rubber's cure profile. In the case of the natural rubber used in thebonding process in the present invention, the rubber was cured for 20minutes at 150° C. under sufficient pressure to ensure intimate contactof the surfaces being bonded and the adhesive.

After curing the bonded samples were aged for 24 hours at roomtemperature before being subjected to testing and the tear patternnoted. Each sample was tested by the 45° angle modified ASTM 429-Bstandard using Instron test equipment (Instron tester, Model No. 5500R)at a steady load rate of 50 mm per minute until separation is complete.

“Rubber coverage” is the percentage of rubber remaining on the bondedmetal substrate after peel testing. 100% rubber failure means that therubber completely failed with no portion of the rubber peeling away fromthe surface of the metal (and equates to 100% rubber failure).

Generally, it is desirable that the rubber substrate fails before themetal to rubber bond fails. The result is achieved with certain of theformulations as set out above.

The words “comprises/comprising” and the words “having/including” whenused herein with reference to the present invention are used to specifythe presence of stated features, integers, steps or components but donot preclude the presence or addition of one or more other features,integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

The invention claimed is:
 1. A bonding composition comprising: at leastone copper compound; and at least one aromatic nitroso compoundprecursor, wherein the aromatic nitroso compound precursor comprises atleast one alkoxy silane moiety.
 2. A composition according to claim 1further comprising an adhesion promoting agent.
 3. A compositionaccording to claim 2 wherein the adhesion promoting agent is a silane.4. A composition according to claim 1 wherein the aromatic nitrosocompound precursor comprises an aromatic oxime, an aromatic dioxime orcombinations thereof.
 5. A composition according to claim 1 wherein thearomatic nitroso compound precursor is mono- or dioxime of a compoundselected from the group consisting of:


6. A composition according to claim 1 wherein the aromatic nitrosocompound precursor comprises a nitrosobenzene precursor, adinitrosobenzene precursor or combinations thereof.
 7. A compositionaccording to claim 1 wherein the copper compound is selected from thegroup consisting of Cu(I) compounds, Cu(II) compounds, Cu(0) compoundswhich may oxidise in situ to a Cu(I) or Cu(II) compound and combinationsthereof.
 8. A composition according to claim 1 wherein the coppercompound is selected from the group consisting of copper nanopowder,CuO, Cu₂O, CuSCN, Cu(SCN)₂ and combinations thereof.
 9. A compositionaccording to claim 1 further comprising a suitable carrier vehicle. 10.A composition according to claim 1 wherein a nitrosobenzene, adinitrosobenzene or a para-nitrosophenol moiety is generated in-situfrom the aromatic nitroso compound precursor.
 11. An assembly comprisinga first substrate and a second substrate bonded together by thecomposition of claim
 1. 12. A cured product comprising an elastomer anda composition according to claim
 1. 13. A process for bonding twosubstrates together comprising applying a bonding compositioncomprising: a. at least one copper compound; and b. at least onearomatic nitroso compound precursor to at least one of the substratesand bringing the substrates together, wherein the aromatic nitrosocompound precursor comprises at least one alkoxy silane moiety.
 14. Aprocess according to claim 13 wherein a first substrate comprises anelastomer to be bonded to another substrate.
 15. A process according toclaim 14 wherein the elastomer is a natural or synthetic rubber.
 16. Aprocess according to claim 15 wherein the aromatic nitroso compoundprecursor is oxidised in situ to an aromatic nitroso compound, whichbecomes anchored to the rubber.
 17. A process according to claim 15wherein the rubber substrate is vulcanised or cross-linked prior tobonding to the metal surface.
 18. A process according to claim 15wherein the rubber is vulcanised or cross-linked concurrently withbonding to the metal surface.
 19. A process according to claim 13wherein a first substrate comprises a natural or synthetic rubber to bebonded to a second substrate and the second substrate is a metallicsubstrate.